    Patent Document 1: JP 2001-006061 A    Patent Document 2: JP 2005-038037 A    Patent Document 3: Abstract of the 2006 IEICE General Conference (CBS-1-6 UHF Band RF Circuits for RF tag with Battery Supply, March 2006)
In recent years, in order to realize safe, worry-free, convenient society in which everyone is able to connect to computer networks everywhere with users unaware of them in particular based on providing information, search, and integration analysis as ubiquitous networks, ubiquitous services, or the sensor fusion, it is considered that it is necessary to improve environment in which various types of sensor tags and functional tags of long lifetime and connectable at radio frequencies can be provided and used as infrastructure.
When this is to be carried out, in the field of wireless connection techniques, in order to read a large number of tags, it is essential that tags operate in a long range and transmit data at high speed. In consideration of operation for a long lifetime, a scheduled start semi-passive tag and a remote start semi-passive tag are preferably used.
The scheduled start semi-passive tag is operated by such a scheme that the scheduled start semi-passive tag is generally in the wait state for a timer with a small power consumption in order to reduce the consumption of an internal battery for startup for regular reception and response operations. However, the tag has a drawback of a poor real time responsiveness.
On the other hand, the remote start semi-passive tag is operated by such a scheme that a power supply is generally in the off state in order to similarly reduce the consumption of an internal battery for startup, and only when RF power is fed from the RF tag reader side, the power feed is used for remote startup (the power supply is turned on). However, although real time responsiveness is excellent, the remote start semi-passive tag has such drawbacks that when the remote start semi-passive tag exists together with a different system (a wireless LAN, a scheduled start semi-passive tag reader, and the like) in the same frequency band, the remote start semi-passive tag repeats unnecessary remote startup in connection with system startup of these systems and accelerates the consumption of the internal battery (for example, see Patent Documents 1 and 2).
Then, in an environment in which wireless LANs, scheduled start semi-passive tag readers, remote start semi-passive tag readers, passive tag readers, and the like exist together for use in the same frequency band, such a remote start semi-passive tag is desired that the consumption of the internal battery can be reduced, even in the state in which any of these systems are used at the same time. In addition, it is desired to realize a radio communication scheme of high transmission rates and various combinations of sensor tag systems and ubiquitous services.
On the other hand, as an RF tag before, as shown in FIG. 1(A) (for example, see Patent Document 3), a normal reception selector switch 3 connected to an input (Pin) 1 through a transmission modulating circuit 2 is connected to a wakeup detecting circuit 4 having a matching circuit 4a and a DC detecting circuit 4b, and the output voltage of the DC detecting circuit 4b is read by a wakeup side A/D converter 5, whereby the presence of RF power feed from an RF tag reader, not shown, is monitored. When RF power feed from the RF tag reader is made, the reception selector switch 3 is switched and connected to the ASK modulated wave reception circuit 6 side, a command sent from the RF tag reader is modulated, the command is read by an ASK modulated wave reception circuit side A/D converter 7 and analyzed by a digital signal processing circuit 8, and a response signal is sent back by repeatedly turning on and off a transmission switch 2a of the transmission modulating circuit 2.
In addition, for the DC detecting circuit 4b used here, as shown in FIG. 1(B), an eight-stage stacked diode detecting circuit is used. In addition, an ASK modulated wave reception circuit 6 has a matching circuit 6a, a reception detecting circuit 6b, a limiter 6c, and an operational amplifier 6d. 
In this startup scheme, because it is necessary to operate the wakeup side A/D converter 5 all the time even though there is no response request from the RF tag reader (RF power feed from the RF tag reader), it is considered that an internal battery (not shown) is consumed soon.
In addition, because the output voltage of the wakeup detecting circuit 4 outputs one volt (load resistance 1 MΩ) at an RF input power of −15.3 dBm, it is assumed that this output is easily used to conduct on/off control of a switch (not shown) for power feed for the entire tag circuitry.